1. Field of the Invention
The present invention relates to a printer for processing print data output from a controller and, more particularly, to a printer for processing print data output from a controller and then inputting the processed data to an engine unit.
2. Description of Related Art
A conventional printer comprises a data processing circuit between a controller which outputs print data and an engine unit where the print operation is executed based on the output print data. The technique concerning the conventional printer is disclosed, for example, in Japanese Laid-Open Patent Publication No. 2-172766 and U.S. Pat. No. 4,847,641 (Japanese Laid-Open Patent Publication No. 2-112966). As the above-mentioned data processing circuit, a circuit has been proposed for inputting the print data output from the controller to the engine unit after being processed, for example, after having the resolution of the data improved.
A printing operation is executed as follows in such a conventional printer. First, the controller instructs an engine unit to feed a printing paper. The engine unit receives the instruction and starts to feed the printing paper. The engine unit returns a feed starting signal of the printing paper to the controller. The controller, upon receipt of the start signal, outputs the print data at the appropriate time when a predetermined amount of the printing paper is sent, i.e., for example, at the time that the printing paper is sent off only for the blank to be provided on the top of the sheet. The output print data is processed as high resolution print data with respect to other print data which exist around it, when the output print data passes through the data processing circuit. The processed print data which has passed through the data processing circuit input to the engine unit. The engine unit then prints a predetermined image according to the input print data.
According to the above-mentioned conventional printer, for example, when the engine unit has a print ability of high resolution of 600 dpi (dots per inch), even if the data output from the controller corresponds only to 300 dpi, the substantial print image of 600 dpi which makes the best use of the efficiency of the engine unit can be obtained by processing the print data to 600 dpi resolution by the data processing circuit.
However, in the above-mentioned conventional printers, the print data output from the controller may pass the data processing circuit so that the data is input to the engine unit later than the predetermined timing. As a result, a problem results in that the position of the image printed on the printing paper shifts from a predetermined position. For instance, an image 19 which should be printed on the center of a printing paper 17 was printed as an image P moved to the lower right as shown in FIG. 4(C) with the two-dash chain line because of the delay of the input of the print data.